1. Field of the Invention
The present invention generally relates to optical semiconductor devices with a window lid, and more particularly to a semiconductor-type projection device.
2. Description of the Related Art
FIGS. 1A and 1B are diagrams illustrating a conventional semiconductor-type projection device 10. According to the semiconductor-type projection device 10, a DMD (digital micromirror device) main body 12 is mounted in a recess 11a on the upper surface of a ceramic substrate 11. A window lid 13 is fixed on the substrate 11 so as to close the recess 11a so that an internal space 14 is hermetically sealed. A window part 15 through which light passes is formed in the window lid 13.
A metal layer 11b is formed around the recess 11a on the upper surface of the substrate 11. The window lid 13 includes a Kovar frame member 16 and a glass plate member 17. As illustrated in FIG. 2F, the frame member 16 includes a frame part 16a and a flange part 16b extending outward therefrom with an opening window 16c formed inside the frame part 16a. The glass plate member 17 is fitted into the opening window 16c inside the frame member 16a. The peripheral surface of the glass plate member 17 is welded to the internal surface of the frame part 16a by matched welding so as to ensure air tightness therebetween. Further, the flange part 16b is seam-welded to the metal layer 11b of the substrate 11 so as to also ensure air tightness. The thickness t1 of the flange part 16b is as thin as 0.25 mm so as to ensure excellent seam welding. As a result, a matched welding part 18 is formed between the peripheral surface of the glass plate member 17 and the internal surface of the frame part 16a, and a seam welding part 19 is formed between the flange part 16b and the metal layer 11b of the substrate 11. Japanese Laid-Open Patent Application No. 2-65190 discloses such a configuration.
Matched welding, which is accompanied by chemical reaction, may generate fine air bubbles or cracks in the glass plate member 17. The fine air bubbles or cracks appear in the window part 15 although in its periphery. Accordingly, light passing through the periphery of the window part 15 is affected by the air bubbles or cracks so as to reflect diffusely. This may affect the characteristics of the semiconductor-type projection device 10. This adverse effect is likely to be produced in particular when the window part 15 cannot be formed to be large in size. Further, the fine air bubbles or cracks exist in a part visible from above the semiconductor-type projection device 10. This impairs the appearance. In the case of viewing mass-produced semiconductor-type projection devices 10 from above, the rate of appearance of fine air bubbles in the window part 15 is 8%, and the rate of appearance of fine cracks in the window part 15 is 4%, which are relatively high.
The length of a seal pass L1 (FIG. 1A) by the matched welding part 18 is obtained by the thickness of the frame part 16a. However, it is difficult to make the thickness of the frame part 16a greater than a predetermined value. As a result, the seal pass L1 is limited to approximately 3 mm, and cannot be longer.
FIGS. 2A through 2F are diagrams for illustrating a process for manufacturing the frame member 16. As illustrated in FIG. 2A, the frame member 16 employs a thick plate material 20 of a thickness t2 of approximately 3 mm as its material. Primary window opening is accomplished by performing blanking on the thick plate material 20 by press working as illustrated in FIG. 2B. Then, as illustrated in FIG. 2C, a peripheral part 16a2 of an initial frame part 16a1 is pressed by stamping so that an initial flange part 16b1 is formed. Further, as illustrated in FIG. 2D, secondary window opening is accomplished by press working so that the opening window 16c is formed. Then, as illustrated in FIG. 2E, the peripheral part of the initial flange part 16b1 is trimmed, and finally, as illustrated in FIG. 2F, the upper and lower surfaces of the trimmed flange part 16b2 are ground so that the trimmed flange part 16b2 has the thickness t1. Thereby, the frame member 16 is manufactured.
The thickness t2 of the plate material 20, which is the material of the frame member 16, is more than ten times the thickness t1 of the flange part 16b. 
Accordingly, the plate material 20 must be pressed greatly in size, so that a large-size stamping machine is required. Further, it is difficult to obtain a predetermined size only by stamping, so that grinding is performed after stamping. This increases the manufacturing cost of the frame member 16.